The present invention is generally in the area of forming new tissues by implantation of appropriate cells on a polymer matrix, and is specifically directed towards construction of new tendons and ligaments.
Tissues connecting bones and muscles are collectively referred to herein as “connective tissue”. Tendons are tissues which attach muscles to bones; aponeuroses are sheet-like tendons connecting one muscle with another or with bones; ligaments hold bones together at joints. Tendons and ligaments are elongated, cylindric structures formed of dense connective tissue, adapted for tension in one direction, with fibers having an orderly, parallel arrangement. The most common variety of dense regularly arranged connective tissue has a predominance of collagenous (white) fibers arranged in bundles. Fibroblasts are placed in rows between the bundles. The tissue is silvery white, tough, yet somewhat pliable. The collagen bundles of the tendons aggregate into larger bundles that are enveloped by loose connective tissue containing blood vessels and nerves. Externally, the tendon is surrounded by a sheath of dense connective tissue.
An essential characteristic of connective tissue is its strength and ability to stretch or be pulled, then regain its original shape. When damaged, the orderly structure which imparts this ability to the connective tissue is disrupted and usually does not heal to yield a fully functional tissue.
Tendon defects, regardless of their origin, often prove to be difficult problems for orthopedic surgery and hand surgery. An ideal reconstruction repairs the defect with an autologous tendon graft. Autogenous tendon usage is limited by availability and donor site morbidity. Consequently, other approaches have been used: homo- or heterografts and artificial tendons. Homo- or heterografts, though, suffer from a scarcity of supply, increased susceptibility to infection, and concerns about possible transmission of infectious agents.
A carbon fiber implant for reconstructing severely torn ligaments and tendons has been developed which consists of carbon fibers coated with a polymer such as polylactic acid, as discussed in “Principles of Human Anatomy” by G. J. Tortora, 5th edition (Harper & Row, NY 1989). The coated fibers are sewn in and around torn ligaments and tendons to reinforce them and to provide a scaffolding around which the body's own collagenous fibers grow. The polymer is hydrolysed within the body over time and the carbon fibers eventually fracture, typically within two weeks. During this time, fibroblasts coat the fibers with collagen. The original structure of the tendons is not maintained, however, and the repaired tendon lacks strength and flexibility. Artificial prostheses, although not infectious, are also susceptible to infection, extrusion, and uncertain long-term immunologic interactions with the host. Moreover, prostheses cannot adapt to environmental stresses as do living tendon tissue and have a high incidence of adhesive breakdown at their interface with the host.
It is therefore an object of the present invention to provide a method and materials for creating new tendons and ligaments which have the strength and flexibility of normal tendons and ligaments.
It is a further object of the present invention to provide a method and materials for creating new tendons and ligaments which leaves no foreign materials in the body nor elicits an immunological reaction against the new tendons or ligaments.
Connective tissue, including neo-tendons and ligaments, has been constructed using biodegradable synthetic scaffolds seeded with tenocytes. The scaffolds are preferably formed from biodegradable fibers formed of a polymer such as polyglycolic acid-polylactic acid copolymers, and seeded with cells isolated from autologous tendon or ligament by means of enzymatic digestion or direct seeding into tissue culture dishes from explants. The cell polymer constructs are then surgically transplanted to replace missing segments of functioning tendon or ligament.
As shown by the examples, transplanted tenocytes attached to biodegradable synthetic polymer scaffolds to generate new tendon in mice. Tenocytes were isolated from freshly slaughtered newborn calf tendon and were seeded onto a non-woven mesh of polyglycolic acid, arranged as either a random array of fibers, or as fibers in parallel. The cell-polymer constructs were implanted into the mice subcutaneously. Specimens were harvested after six to ten weeks and examined. On gross examination, all specimens closely resembled tendons from which the cells had initially been isolated. Histologic evaluation demonstrated that collagen bundles appeared to be organizing in a parallel fashion at the lateral aspects and appeared very similar to the collagen bundles seen in normal tendon. Centrally, the collagen fibrils appeared to be randomly oriented. Specimens that were created from implantation of parallel polymer fibers appeared to have a greater degree of parallel collagen fibril orientation at an earlier time period. The neo-tendon constructs demonstrated moderate tensile strength when stretched.